The present invention relates to manufacturing of a golf ball, and more particularly, to the method of dimple arrangement capable of improving formability and performance of a golf ball simultaneously, and the golf ball thereof.
Generally, it is known that straightness, consistency, carry distance and so on, used as a measure of performance of a golf ball, are greatly affected by aerodynamic action depending on the size, depth, shape, arrangement of dimple formed on a surface of a golf ball.
Specifically, when a golfer hit a golf ball, strong repulsive elasticity is generated and launching the ball, at the same time back spin is generated by the loft angle of a golf club. For example, if the club is 10 degree driver, the impacted ball will fly away and also be formed the back spin of approximately 2200˜4000 revolutions per minute at an initial state. At the moment, the dimples accelerate the transition of turbulent air flow around the boundary layer of a rotating ball surface in flight through the high speed air stream, in the meantime, the air pressure will increase beneath the reversed rotating ball whereas it decrease above the ball, as a result, aerodynamic lift equivalent to many times of gravity is generated due to the Bernoulli effect, that extends the carry distance of a golf ball.
Moreover, it lowers a coefficient of drag even at a low speed area by reducing the Critical Reynolds Number. But the speed and rotational strength of the ball does not maintain as initial state of hitting, they rapidly reduce from the peak of a ballistic trajectory to the landing point Which is called as a low speed area, accordingly the Critical Reynolds number will rapidly increase and a coefficient of drag as well.
Meanwhile, the dimples being arranged by dividing the outer surface of a golf ball into the faces of a spherical polyhedron with the great circle paths that has a symmetry of left and right side of a golf ball. That spherical polyhedron is, for instance, spherical tetrahedron composed of 4 spherical triangles, spherical hexahedron composed of 6 spherical squares, spherical octahedron composed of 8 spherical triangles, spherical cube-octahedron composed of 6 spherical squares and 8 spherical triangles, spherical icosahedron composed of 20 spherical triangles, spherical icosi-dodecahedron composed of 20 spherical triangles and 12 spherical pentagons, and so on. There are many kinds of the dimple arrangement of the divisional composition of the surface of a golf ball into the faces of a spherical polyhedron by this manner. As a reference, FIG. 1 and FIG. 2 illustrate plane view of a golf ball that dimples being arranged on the spherical cube-octahedron and spherical icosi-dodecahedron respectively among the spherical polyhedron.
In this regard, recently the circular dimples are used a lot in general, the important matters of the dimple arrangements are volume ratio by it's depth of dimple and area ratio of dimples coverage on the surface of a golf ball. In case of volume ratio of dimples on the surface of a golf ball having circular dimples, which has a correlation with the area ratio of dimples on its surface due to the definite size of a ball, it is impossible to make cavities for cover mold allowing to freely change the volume of dimples by ignoring the area of dimples except the required volume ratio for obtaining fundamental aerodynamic lift, that due to the material and metal working for cover mold cavity which arranged the dimples directly. Therefore, if the area ratio of dimples corresponds to about 75%˜84% of the total surface area of a golf ball having circular dimples, the total volume of dimples on its surface will be around 350 mm3˜490 mm3. A volume ratio becomes proportional to the area ratio of dimples, that is, increasing the diameter of dimple results in a larger volume of dimple, and decreasing the diameter of dimple results in a smaller volume of dimple.
For convenience' sake, if a diameter of dimple is more than 0.15 inches (3.81 mm), that is called a large sized dimple, a diameter of dimple is smaller than 0.15 inches, called a small sized dimple. If hit a golf ball, large sized dimple lowers a coefficient of drag in a low speed area whereas it raise the coefficient of drag in a high speed area, on the contrary, small sized dimple lowers a coefficient of drag in a high speed area, but it tends to raise the coefficient of drag in a low speed area. But, the small sized dimple aid the aerodynamic stability. Drag which mentioned above is a combination of pressure drag and friction drag. The strength of pressure drag is affected by the shape, size of the substance and the stream direction, speed against it, whereas the strength of friction drag varies with the shearing strength caused by the viscosity of fluid flow the surface of the substance and the roughness of the surface of the substance. And a coefficient of drag varies with the Reynolds number, in case of a golf ball, there is no problem in terms of a carry distance and a stable flight at a high speed area from the hitting point to the apex of the ballistic trajectory, because a coefficient of drag diminish as the Reynolds number grows in that area. But the problems occurred in a low speed area from the apex of the ballistic trajectory to the landing point when decreasing the hitting power.
Meanwhile, recently it tends to make the dimple size have some similarities each other in a diameter by reason of an appearance of a golf ball, total number of dimples are get fewer 300˜400, the composed size of dimple diameter get bigger than 0.15 inches inevitably, which the trajectory is seriously affected in accordance with the flow direction of the air. In addition, the carry distance is the first consideration in development of a golf ball which has an irrespective aerodynamic direction and the flight stability in dimple arrangement, which cause so many problems.
And, in order to raise the area ratio of dimples on the surface of a golf ball, or the reason of an appearance of it, the dimple arrangement is depart from the border and miss matched each other on the border of each polygon (for example, the spherical triangles and the spherical squares which composed of a spherical polyhedron in cube-octahedron) of the polyhedron, as a result of it, the mold parting line which the meeting line of the upper mold and bottom mold, that is not a straight line as the great circle paths which divide the surface of a golf ball into the faces of polyhedron, being a kind of meanderingly wave line with a regular continuity or discontinuity wave line. In addition, there is a type of zigzag line in actuality.
Specifically, the manufacturing of mold becomes very difficult for making cover with an accurate symmetry between right and left side of the dimples of these golf balls. The difficulty of manufacturing mold, firstly, the matching of upper mold and bottom mold correctly which have same kind of a mold parting line with the meanderingly wave line, secondly, it is very difficult to make the gate size evenly and settle the gate position correctly for flowing the polymer materials uniformly which forming the cover of the golf ball. For example, as shown in FIG. 3, if dimples 12a˜12o are arranged by the boundary of great circle 13 forming an equator of a golf ball, a wave type mold parting line 14 is formed. And this wave type mold parting line 14 occupied 100% of the line composed the circumference of a circle as a straight line.
Therefore, it is difficult to form gates 15, 16, 17, 18 due to the narrow gap of dimples between upper and bottom side. And the size of the gates becomes so smaller that it is difficult to flow resin regularly. Also, the excessive pressure inflicted on the resin by an enforced passing through the smaller gate, that cause the phenomena of resin being decomposed, and the weld—lines by an unsealing molding of the polar region due to the clogged vent pin which exhaust the gas like materials, the burning phenomena which the resin being partially burned by the high pressure, and the cover filled with the gas. That is the seriously inferior phenomena, the cover has not a uniformly thickness and being an inferior appearance.
Meanwhile, if the molding by maintaining the holder pin for a long time for preventing an eccentricity of insert one which inserted in the cavity as a half finished goods, such as a core, dual core, the mantle covered the said core and inner cover until the resin get firmer, that achieved the inferior cover molding of a collapse, crack and something like this. By the inferior phenomena, a finished product having an undesirable appearance and which being split easily.
And, after treatment of the cover molding which made by using a mold in a hard way, for example, the removal of the gates and the remains of resins which flowing out from the edge of the mold parting line, the buffing (the treatment by using a cutter, sand paper and a sand stone) process for eliminating the interior part of molding near the vent pin and the polar region, a variation of the size of equator region, a difference between the size of equator to equator and pole to pole by an immoderate buffing due to the irregular parting line, or the dimple depth may be shallower and the polar region may be irregularity by that reason, which is changed the aerodynamic characteristics of the golf ball, and it has the unsettled landing point from the apex of the ballistic trajectory.
Meanwhile, a kind of golf ball, which has a dimple on the pole, and as shown in FIG. 4, the mold parting line 24 same as the straight line of the great circle path 23, that arranged the gates 25, 26, 27, 28 on the upper and bottom side of the mold parting line 24 in regularity, there is no problem for making the cavity mold, and in the after treatment process, the productivity is good for reducing the inferior phenomena of molding by the easy buffing process, but there is a limit for raising the area ratio of dimples of the surface of a golf ball basically.